Permeability Determination in Carbonate Rocks Integrating Nuclear Magnetic Resonance, Acoustic and Formation Test Data

Abstract

Abstract

Permeability is one of the main petrophysical parameters for determining the producibility of a reservoir. The determination and correlation of this property using well logs is very challenging, particularly in carbonate rocks because of their complex texture and morphology. Also, permeability cannot be measured directly in the wellbore by either wireline or LWD technologies. Various models and correlations are usually used to infer permeability from the data of various logging tolls. The models and correlations must be calibrated by laboratory results to determine parameters that correspond to various lithologies and formation types.

NMR provides the preferred data to estimate a continuous permeability log. One of the most common models is the Timur-Coates equation. The parameters of this equation, however, must be calibrated, e.g., by laboratory results. Acoustic logs provide data to calculate permeability from Stoneley waves which also incorporate parameters adjusted by laboratory results. One challenge in permeability evaluation is that core plugs are often not available or their laboratory analysis is time-consuming and costly. Therefore, default values for the parameters are used, which can lead to deviations and offset in the estimated permeability, especially in complex carbonate rocks.

Permeability can also be determined from formation test tools which measures the reservoir pressure, but also enables for fluid sampling and downhole fluid characterization. In addition to pressure, the tool provides information about mobility. This mobility can be used to infer permeability, because permeability is the product of mobility with viscosity.

This paper presents an approach to integrate permeability, derived from NMR and acoustic data, with formation test analysis, to provide a calibrated continuous permeability curve across carbonate reservoirs where core sample results are not available. The workflow includes using the formation test permeability to adjust the parameters of either the NMR and/or acoustic equation to improve the petrophysical characterization of the reservoir. By combining the three methods, a robust and accurate model for carbonate rocks is generated to provide improved formation permeability. Some examples from real field data examples are presented, where the value is demonstrated of integrating the formation test permeability with NMR and acoustic permeability in carbonate formations.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016